Apparatus and process for the electrofracing of oil sand formation through a casing



Feb. 22, 1966 E. SARAPUU APPARATUS AND FROG ESS FOR THE ELECTROFRACING OF OIL SAND FORMATION THROUGH A CASING 2 Sheets-Sheet 1 Filed Sept. 1, 1961 Feb. 22, 1966 E. SARAPUU 3,236,304

APPARATUS AND PROCESS FOR THE ELECTROFRACING OF OIL SAND FORMATION THROUGH A CASING Filed Sept. 1, 1961 2 Sheets-Sheet 2 INVENTOR.

United States Patent Office 3,236,304 Patented F eh. 22, 1966 3,236,364 APPARATUS AND PROCESS FOR THE ELECTRG- FRACING OF OIL SAND FORMATION THRQUGH A CASING Erich Sarapuu, 7943 Campbell, Kansas City, Mo. Filed Sept. 1, 1961, Ser. No. 135,655 9 Claims. (Cl. 166-35) This application is a continuation-in-part of my application Serial No. 123,529, filed July 12, 1961 Single Wellbore Coking Means and Processes, now abadoned, and my application Serial No. 103,429, filed April 17, 1961 entitled Single Well Subsurface Electrification Means and Process, now abandoned.

This invention is directed to new and useful improvements in apparatus and processes for the electrofracing of oil sand formations through a casing and more particularly to apparatus and processes for perforating the casing of a borehole and thereafter heating the area surrounding the borehole or electrolinking adjacent boreholes, and electrocarbonization and electrogasification of the fuel bearing strata adjacent the borehole.

This application and invention is an improvement over my Patent 2,795,279, issued July 11, 1957.

Prior to the present invention, in the preparation of an oil well, a hole was first bored down into the oil bearing strata and a steel casing was then inserted into the hole. The next step was to perforate the steel casing adjacent the oil bearing strata to permit the passage of fluid through the casing. This has been accomplished in the past by various means but principally by devices that fire bullets or pellets against the inside wall of the casing to puncture it.

The present invention provides novel means and processes for perforating the casing and simultaneously heating the area surrounding the casing to prevent solidification of various parafiins which might possibly clog the openings in the casing or the casing itself and also permit either at the time the well is drilled or later, electrocarbonization and, if desired, electrogasificat-ion of the fuel in the oil bearing strata.

With the foregoing in mind, a primary object of the present invention is to provide novel apparatus and processes for permitting the perforation of a steel casing and a borehole or oil well and either simultaneously with the perforation or at some later time permit electrocarbon-ization and electrogasification of the fuel in the fuel bearing strata.

Another object of the present invention is to provide a novel apparatus for perforating the walls of the steel casing of a borehole or oil well and to provide means for permitting pressurizing fluid to be used for cleaning out the holes and the surrounding area so that fluid can easily enter the casing.

Another object of the invention is to provide apparatus for and methods of electrolinking paired wellbores communicating with a single fuel strata where said paired wellbores are cased through or in the said fuel strata.

Another object of the invention is to provide means for electrically communicating paired wellbores in a single fuel strata where the said wellbores are cased in the vicinity of the fuel strata and also permitting the passage of fluids from the fuel strata into the said wellbores or out of the wellbores into the said fuel strata.

Still another object of the invention is to provide means and processes of selectively electrically perforating steel casings in wellbores adjacent fuel strata, the means and methods permitting sequential or simultaneous perforations vertically spaced from one another or radially spaced from one another or both.

Another object of the invention is to provide means for electrically perforating steel casings in wellbores and communicating with the fuel strata therebeyond, said means not only permitting electrical penetration of the casing and communication with the fuel strata therebeyond, but also permitting withdrawal of the electrode from the perforation for further perforation and communication, but also providing access for fluids from the fuel strata into the wellbore or access for fluids from the wellbore into the fuel strata.

Another object of the invention is to provide electrical means and processes, including electrical circuits, for perforating cased wellbores and electrically linking same.

Another object of the invention is to provide means which permit the electrical penetration and treating of a formation from -a single cased wellbore, such electrical penetration for permeability increase or wellbore coking.

Other and further objects of the invention will appear in the course of the following description.

In the drawings, which form a part of the instant specification and are to be read in conjunction therewith, embodiments of the invention are shown and, in the various views, like numerals are employed to indicate like parts.

FIG. 1 is a diagrammatic View of a borehole entering a fuel bearing strata with the apparatus of the present invention applied thereto.

FIG. 2 is an enlarged side elevational view partially in section of one form of apparatus made in accordance with the present invention.

FIG. 3 is a schematic cross-sectional view through an earth formation showing two wellbores therein communicating with a single fuel strata, apparatus of the present invention applied into both wellbores for easing penetration and electrical linking therein.

FIG. 4 is an enlarged side elevational view, with parts cut away and in section better to illustrate the construction of the electrodes employed in FIG. 3.

Referring more specifically to the drawings, reference numeral 10 designates generally a strata of underground fuel such as an oil sand strata with a borehole 11 extending into the strata of fuel. A steel casing 12 is provided within the borehole and a hollow tubular member 13 extends downwardly into the borehole centrally of the steel casing 12 and terminates adjacent the fuel bearing strata 10. A cap 14- formed of insulating material is provided at the top of the borehole 11 and serves to po sition the tubular member 13 within the borehole and electrically insulate the tubular member from the casing 12 and the surrounding ground area.

In accordance with the present invention a plurality of electrodes 15 are carried by the lower end of the tubular member 13 and are adapted to be forced outwardly into engagement with the steel casing 12' to perforate the casing and heat the area of the fuel bearing strata 10 surrounding the casing. The electrodes 15 preferably are carbon electrodes carried by a cylindrical metal base member 16, which is slidably mounted in a sleeve 17. The sleeve 17 in turn is supported within a ceramic casing 18 within which a hollow metal spool 19 is embedded. The spool terminates short of the bottom of the ceramic casing 18 and is secured to the lower end of the tubular member 13, for example, by means of a plurality of bolts 21). A cap 21 is provided over the outer end of each sleeve 17 to engage the base member 16 of each electrode 15 and limit forward movement of the electrode 15'. The electrodes 15 preferably are spring-loaded to be projected toward their outer or extended position for example, by means of a spring 22 positioned within each sleeve 17 and in engagement with the rear surface of each base member 16.

With this above construction after the well or borehole has been drilled, the tubular member 13 carrying the ceramic casing 18 and electrodes is lowered into the well or borehole with the electrodes 15 spring biased outwardly against the inner surface of the well casing 12. When the electrodes reach the desired location adjacent a fuel bearing strata 10, electric current is supplied to the electrodes causing the electrodes to burn openings 23 through the wall of the casing 12 and also heat the area in the fuel bearing strata 10 surrounding the well casing 12. Electric current is provided to the electrodes from a suitable source of current such as a transformer 24 and voltage regulator 25 through a switch 26 and a pair of leads 27 and 28. One lead 27 goes to a terminal 29 secured to the tubular member 13 while the other lead 28 is connected to a terminal 30 embedded in the ground adjacent the wall or borehole. The terminal 29 is interconnected with the electrodes through the electrode base 16, spring 22, spool 19 and tubular member 13, all of which are made of an electrically conductive material such as steel.

After openings have been burned or formed in the wall of the metal casing 12, it may be desirable or necessary to clean the hole in the casing and the area of the fuel bearing strata 10 surrounding the casing by forcing fluid under pressure outwardly through the openings. To accomplish this, openings 31 are provided in the core of the spool 19 in fluid communication with the interior of the sleeves 17 and the core of the spool 19 is placed in fluid communication with the interior of the tubular member 13. A suitable fluid under pressure is then admitted to the interior of the tubular member 13 and the fluid passes downwardly through the tubular member into the core of the bore 19. Thereafter, the fluid passes outwardly into the sleeve 17 and through openings 33 provided centrally of each electrode 15. The fluid under pressure may be used to maintain the openings 33 in the electrode open and also maintain the area surrounding each electrode 15 open. Additionally, fluid from the fuel bearing strata 19 may be permitted to escape through the well by passing through the openings 33 in the electrodes and then upwardly through the tubular member 13.

After the openings have been burned or cut in the wall of the well casing 12, passage of electrical current to the electrodes 15 may be maintained causing the electrodes to heat the surrounding area of the fuel bearing strata 1t and cause electrocarbonization of the fuel in the fuel bearing strata 10. Additionally, heated air or steam may be supplied through the tubular member 13 in addition to the heat supplied by the electric current discharged from the electrodes 15 to cause electrogasification of the area of the fuel bearing strata 10 surrounding the well casing.

Referring to FIG. 3, numeral designates a strata of underground fuel such as an oil sand strata with a borehole 41 extending into the strata of fuel. The right-hand well in the figure will be first described. A steel casing 42 is provided Within the borehole and a hollow tubular member 43 extends downwardly into the borehole centrally of the steel casing 42 (centralizers may be used as required of an insulating material) and terminates adjacent the fuel bearing strata 40. A cap 44 formed of insulating material is provided at the top of the borehole 41 and serves to concentrically position the tubular member 43 within the borehole and electrically insulate the tubular member from the casing 42 and the surrounding ground area.

In accordance with the present invention, at least one electrode 45 is carried by the lower end of the tubular member 43 and is adapted to be forced outwardly into electrical contact or physical engagement with the steel casing 42 to perforate the casing and penetrate the area of the fuel bearing strata 40 surrounding the casing. Additionally, electrical current may be conveyed into the formation for purposes to be described. The electrode 45 preferably is a carbon electrode carried by a cylindrical metal base member (see FIG. 4) which is slidably mounted in a sleeve 47. The sleeve 47 in turn is supported within a ceramic casing 48 Within which a hollow metal spool 49 is embedded. Spool 49 terminates short of the bottom of the ceramic casing 48 and is secured to the lower end of the tubular member 43, for example, by means of a plurality of bolts 50. A cap 51 is provided over the outer end of the sleeve 47 adapted to engage the base member 46 of the electrode 45 and limit forward movement of the electrode 45. Electrode 45 preferably is spring loaded to be projected toward its outer or extended position, for example, by means of a spring 52 positioned within each sleeve 47 and in engagement with the rear surface of each base member 46.

In the modification of the invention shown, the tapered end 45a of the electrode is preferably substantially the only portion thereof that may be extruded beyond the cap 51 whereby picking up of the tubing 43 or rotation thereof after casing perforation will not snap off the electrode and will permit it to be positioned at a different Vertically or radially spaced position from the original perforation. On the other side of the ceramic casing 48 is positioned an extension 53 on which is mounted a plastic or other resilient insulating material cap 54 whereby to provide a rugged insulated spacer opposed to the electrode whereby to maintain the latter in contact with the casing wall which is desired to be perforated.

Part of the well completion to the left in FIG. 3 identical to those of the right-hand completion are numbered the same but primed.

With the above construction, after the wellbore has been drilled and the casing 41 set therein, the tubing 43 carrying the ceramic casing 48 and electrode 4-5 is lowered into the borehole inside of the casing with the electrode 45 springing back outwardly against the inner surface of the well casing 42. When the electrode reaches the desired location adjacent the fuel bearing strata and when the corresponding electrode in the opposite wellbore has reached a like position, electrical current is supplied to the electrodes causing them each to burn an opening through the respective walls of the casing. Thereafter electrical current may be applied to the oil sand or fuel strata therethrough. This heats the oil sand and causes the effects described in my previous applications and patent noted above, supra.

Electrical current is provided to the electrodes from a suitable source of current such as a transformer 54 and voltage regulator 55 through a switch 56 and a pair of leads 57 and 58. One lead 57 goes to a terminal 59 secured to the tubular member 13, while the other lead 58 is connected to a terminal secured to the other tubular member 43. The terminal 59 is interconnected with the electrode in the right-hand well through the electrode base 46, spring 52, spool 49 and tubular member 43, all of which are made of an electrically conductive material such as steel.

Fluid passage from the formation into the tubing may be achieved through the perforated electrode, as may fluid passage from the tubing into the formation through the casing. If the electrode opening is of sufiicient size and the electrode of a suffiicent strength, with suitable seal means, fracturing or pressuring of the formation through the electrode can be accomplished.

In a first variation of the process using the apparatus of FIGS. 3 and 4, once the casing has been perforated at both wells, sufiicient current is flowed through the two electrodes to electrically link and/ or electrofrac according to the teachings of the above applications therebetween. Secondly, one or both electrodes may be vertically displaced relative to the original perforations and electro linking and a second perforation and electrolinking carried out. Naturally, in such case, the current will be shut off during the vertical transfer of one or more electrodes. In this manner, one formation may be electrolinked at a plurality of vertically spaced positions whereby to increase permeability in a lesser permeability situation. Alternatively, both wells may be vertically electrolinked across the face of the fuel strata for the same purpose simultaneously using several electrodes as in FIGS. 1 and 2, the electrodes, however, on one side of the casing vertically spaced. Fluid may be flowed through the electrodes during the process of electrolinking whereby to provide underground cracking in the manner of my previous application Serial No. 42,401, filed July 12, 1960 entitled Underground Cracking of Mineral Fuels, and now abandoned.

The apparatus of FIG. 4 may be employed in conjunction with a surface ground circuit, that is, a surface ground element tied to the other end of the electrical circuit as in FIG. 1, whereby to coke the fuel strata adjacent the wellbore on the side perforated by the electrode. In case circumferential coking is desired, the circuit of FIG. 1 may be employed. If directional coking is desired, a single electrode apparatus as in FIG. 4 is best. The tip paratus of FIG. 4 may be vertically raised and lowered to coke selectively or across the face of the formation, as desired. It may additionally or simultaneously be rotated inside the casing for radial spacing of perforations.

In certain circumstances the casing may be sheathed with insulating material in its length down to the fuel strata or cemented as seen in FIG. 3 with a relatively nonconductive cementitious material to aid control of the flow of electrical power.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the apparatus and process.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to interpreted as illustrative and not in a limiting sense.

Having thus described my invention, I claim:

1. Apparatus for perforating the casing of a borehole or the like adjacent fuel bearing strata comprising a tubular support member extending longitudinally of said borehole and terminating at the fuel bearing strata, at least one electrode carried by the lower end of said tubular member adjacent said fuel bearing strata and in engagement with said casing, means defining a passageway extending through said electrode, said passageway being in fluid communication with the interior of said tubular member, and an electric circuit interconnected with said electrode to energize said electrode and cause said electrode to perforate said casing and heat the fuel bearing strata adjacent said casing.

2. Apparatus for perforating the casing of a borehole or the like adjacent fuel bearing strata comprising a tubular support member extending longitudinally of said borehole and terminating at the fuel bearing strata, at least one electrode positioned adjacent the lower end of said tubular member, means resiliently mounting said electrode on said tubular member for movement in a direction substantially radially of said tubular member, said mounting means normally urging said electrode radially outwardly away from said tubular member into engagement with said casing, and an electric circuit interconnected with said electrode to energize the electrode and cause said electrode to perforate said casing and heat the fuel bearing strata adjacent said casing, said tubular member electrically insulated from said casing and forming a part of the electric circuit for said electrode.

3. The method for perforating the casing of a borehole and the like and heating fuel bearing strata surrounding said borehole comprising the steps of positioning an electrode within the well casing at the fuel bearing strata,

engaging the casing with said electrode, supplying electric energy to said electrode and causing said electrode to perforate said casing, and continuously supplying a predetermined amount of electric energy to said electrode after the perforation of said casing to heat the fuel bearing strata surrounding the casing.

4. The method as in claim 3 including the step of supplying fluid under pressure to said electrode after the perforation of said casing and forcing the fluid through said electrode and out through said perforation.

5. A method for perforating the casing of a wellbore communicating with underground fuel strata comprising the steps of positioning an electrode within the wellbore casing adjacent the fuel bearing strata, establishing an electrical circuit between a surface ground adjacent the wellbore and said electrode, supplying electrical energy to said circuit whereby to cause said electrode to perforate the casing and come into electrical contact with said fuel strata.

6. A process for communicating an electrode with fuel strata through a well casing and maintaining said cornmunication comprising the steps of drilling a wellbore into a fuel strata, running a casing into said wellbore into said fuel strata, running a hollow tubing into said casing adjacent said fuel strata having a hollow electrode thereon, connecting an electrical power circuit to said electrode whereby to apply electrical energy to said casing, perforating said casing by application of electrical energy thereto through said electrode, and flowing fluid through said tubing and perforated electrode thereon into said casing opening and into said fuel bearing strata around said casing.

7. A process as in claim 6 including stopping the flow of fluid through said hollow electrodes and producing fuel strata fluids through said hollow electrode into said tubing.

8. A process of radially perforating a casing at a plurality of positions with a lesser number of electrodes than the number of perforations comprising drilling a wellbore into an earth formation into a fuel strata, running a casing in said wellbore into said fuel strata, positioning an electrode Within said casing opposite said fuel strata at a first radial position, supplying suflicient electrical energy to said electrode to penetrate said casing at a first radial position, ceasing supply of electrical current to said electrode, rotating said electrode in said wellbore casing to a second radial position, applying suflicient electrical energy to said electrode to perforate said casing at said second radial position.

9. A process of increasing permeability in fuel strata comprising drilling a wellbore through the earth formation containing the fuel strata into said fuel strata, running a casing in said fuel strata, positioning an electrode into said fuel strata within said casing, establishing a surface electrical ground sufficiently far from said wellbore to avoid arcing between the ground and the said casing and connecting electrical power circuits between said surface ground and said electrode, flowing electrical energy between said ground and said electrode whereby to perforate said casing and flowing additional electrical current into said circuit whereby to electrically link said surface ground and said electrode.

References Cited by the Examiner UNITED STATES PATENTS 2,398,868 4/1946 Stuart et a1. 324-10 2,400,678 5/1946 Archie 324-10 X 2,795,279 6/1957 Sarapuu 166-11 CHARLES E. OCONNELL, Primary Examiner.

NORMAN YUDKOFF, BENJAMIN HERSH,

Examiners. 

1. APPARATUS FOR PERFORATING THE CASING OF A BOREHOLE OR THE LIKE ADJACENT FUEL BEARING STRATE COMPRISING A TUBULAR SUPPORT MEMBER EXTENDING LONGITUDINALLY OF SAID BOREHOLE AND TERMINATING AT THE FUEL BEARING STRATA, AT LEAST ONE ELECTRODE CARRIED BY THE LOWER END OF SAID TUBULAR MEMBER ADJACENT SAID FUEL BEARING STRATA AND IN ENGAGEMENT WITH SAID CASING, MEANS DEFINING A PASSAGEWAY EXTENDING THROUGH SAID ELECTRODE, SAID PASSAGEWAY BEING IN FLUID COMMUNICATION WITH THE INTERIOR OF SAID TUBULAR MEMBER, AND AN ELECTRIC CIRCUIT INTERCONNECTED WITH SAID ELECTRODE TO ENERGIZE SAID ELECTRODE AND CAUSE SAID ELECTRODE TO PERFORATE SAID CASING AND HEAT THE FUEL BEARING STRATA ADJACENT SAID CASING.
 5. A METHOD FOR PERFORATING THE CASING OF A WELLBORE COMMUNICATING WITH UNDERGROUND FUEL STRATA COMPRISING THE STEPS OF POSITIONING AN ELECTRODE WITHIN THE WELLBORE CASING ADJACENT THE FUEL BEARING STRATA, ESTABLISHING AN ELECTRICAL CIRCUIT BETWEEN A SURFACE GROUND ADJACENT THE WELLBORE AND SAID ELECTRODE, SUPPLYING ELECTRICAL ENERGY TO SAID CIRCUIT WHEREBY TO CAUSE SAID ELECTRODE TO PERFORATE THE CASING AND COME INTO ELECTRICAL CONTACT WITH SAID FUEL STRATA. 